How does a water filter work? Wouldn't the water get dirty because of the charcoal?

Water filters use a variety of different media (the components of the filter) to reduce contaminants from water. Charcoal is a common media for many water filters. To answer this question simply, a charcoal filter does not make water even dirtier because the charcoal used in water filters is generally solid or granulated (like grains of sand) and not ashy like the charcoal used in art pencils. In a water filter, as water passes over the media, the granules of that media trap large water contaminants and stop them from passing through with the water. The process is very similar to river water passing through rocks and emerging cleaner on the other side.

While this method of filtration is certainly useful, it is not perfect. Water filters can only reduce certain contaminants and smaller contaminants will easily pass through the granules of the media with the water. Most modern filters now use chemical processes to filter water, in addition to simple physical filtration. Modern filters use a media that will attract contaminants (using a process of positive and negative charges similar to magnets) and encourage these contaminants to break their bond with water. For example, chlorine is a chemical that often contaminates water. Chlorine is very difficult to remove by simply passing water over a granular media. Chemically, chlorine can be removed by using a carbon-based media to attract atoms of chlorine and to encourage these atoms to break their bond with the water.

To sum it all up, water filters reduce contaminants by either physically blocking their passage through the filter media or chemically attracting them to the filter media. In general, they use a granulated or solid filter media that will not travel with water and further dirty it.